Downloaded from https://www.everyspec.com MIL-STD-1311D NOISE AND MICROPHONICS METHOD 2201 (Receiving tubes) 1. Test circuit. The basic circuit for the noise and microphonics test is shown on figure 1 of Drawing 194-JAN. In this circuit, the TUT is connected in a resistance coupled amplifier circuit. The circuit constants Rk, Rg1, Rg2, and Rp, and applied electrode voltages shall be those values as specified by tube type on the specification sheet. The value of Eb under test conditions shall be regarded as Ebb for this test. 2. Equipment components. The principal components of this equipment, as shown on Drawing 194-JAN, are described as follows: a. Calibration circuit.
The calibration circuit (Ecal) is provided for selecting the specified signal voltages on each specification sheet. The calibration circuit used for this purpose shall have a range of 0 to 1,000 mV and shall be capable of supplying any calibrating voltage in this range with an accuracy of ± 2.0 percent (see figure 2201-1). b. Cathode follower and noise and microphonics amplifier. The anode of the TUT shall be coupled to the input of the cathode follower which may be located either in the test chassis as shown on the drawings or in the noise and microphonics amplifier.
The response of the cathode follower and amplifier shall be within ± 0.5 dB of the response at 400 Hz over the frequency range of 50 to 5,000 Hz and have a 6 dB per octave maximum cutoff rate in the ranges 20 to 50 Hz and 5 to 20 kHz. The response shall be measured at the anode terminal of the test socket with a generator having an output impedance of 10,000 ohms, or less. The actual input resistance of the cathode follower shall be 1 Meg in parallel with a distributed circuit capacity of 80 ± 10 pF. The power amplifier shall have a power capability of 3 watts minimum at a point of 3 percent harmonic distortion. The hum and noise level shall be at least 30 dB below rejection level.
Below the 3-watt level, the output voltage shall not fall more than 3 dB when going from no load to full load over the frequency range of 50 to 5,000 Hz. The output to input voltage ratio of the cathode follower and amplifier shall be linear within ± 5.0 percent over the output power range of 0 to 3 watts. c. Speaker. The speaker shall be an 8-inch commercial dynamic type with a rating of at least 2.5 watts. The speaker shall be coupled to the output of the amplifier so as to present rated load to the amplifier. The speaker may be mounted in accordance with figure 2 of Drawing 194-JAN and shall be positioned in such a manner that acoustic and mechanical feedback to the TUT is at a minimum.
d. Output meter. The output indicator shall be a VU meter with the rejection level set at the meter reading obtained during calibration. e. Mechanical tapping device. A mechanical tapping device shall be used for mechanically exciting the TUT during noise and microphonics testing. This tapper consists of a motor driven cam actuating an overbalanced lever which delivers an impact to a suspended platform upon which an adapter and the TUT are mounted. The platform shall be tapped at the rate of 120 taps per minute.
The details of the mechanical parts of the tapper and of the adapter box for mounting the TUT are as shown on figure 3 of Drawing 194-JAN and must be standardized so that good correlation will exist between data taken on different equipment. f. Mallet. (Not shown on drawing.) The mallet used for manual tapping shall be as specified in method 1201 (tapping). The mallet may be equipped with a conductive coating. METHOD 2201 2201-1 19 April 1968